extract_parameters() silently fails when extra_delimiters contains regex metacharacters

[ananotherdeveloper]

Version
v0.9.11 (latest release), also present on master

Summary

extract_parameters() uses re.sub(delimiter, " ", log_message) (regex replacement) to preprocess delimiters, while get_content_as_tokens() uses content.replace(delimiter, " ") (literal replacement).
When a delimiter is a regex metacharacter (e.g. "."), template mining succeeds but parameter extraction silently returns None.

Root Cause

Two methods handle the same extra_delimiters config inconsistently:

┌─────────────────────────┬───────────────────┬──────┬─────────────────────────────────────┬─────────────────────┐
│ Method                  │   File            │ Line │Code                                 │ Treats delimiter as │
├─────────────────────────┼───────────────────┼──────┼─────────────────────────────────────┼─────────────────────┤
│ get_content_as_tokens() │ drain.py          │ 306  │ content.replace(delimiter, " ")     │ Literal string      │
├─────────────────────────┼───────────────────┼──────┼─────────────────────────────────────┼─────────────────────┤
│ extract_parameters()    │ template_miner.py │ 214  │ re.sub(delimiter, " ", log_message) │ Regex pattern       │
└─────────────────────────┴───────────────────┴──────┴─────────────────────────────────────┴─────────────────────┘

Introduced in commit 2a363a2 (PR #52, Jan 12 2022) by Ovi T, co-authored by David Ohana.

Reproduction

from drain3 import TemplateMiner
from drain3.template_miner_config import TemplateMinerConfig

config = TemplateMinerConfig()
config.drain_extra_delimiters = ["."]  # dot as delimiter 
tm = TemplateMiner(None, config)

# Step 1: Mine templates — works fine 
tm.add_log_message("app.server status.ok code.200") 
tm.add_log_message("app.server status.ok code.404") 
result = tm.add_log_message("app.server status.err code.500")
template = result["template_mined"] 
print(f"Template: {template}")  # contains <*> — mining succeeded 

# Step 2: Extract parameters — silently fails 
params = tm.extract_parameters(template, "app.server status.err code.503")
print(f"Params: {params}")  # None — extraction failed on a line it just clustered

Why it fails: re.sub(".", " ", "app.server status.err code.503") treats . as the regex wildcard (matches any character), turning the entire message into spaces. The template regex then can't match.

Why mining works: get_content_as_tokens uses str.replace(".", " ") which only replaces literal dots — correctly producing tokens ["app", "server", "status", "err", "code", "503"].

Affected delimiters

Any regex metacharacter used as a delimiter: ., +, *, ?, ^, $, |, (, ), [, {, \

Suggested Fix

template_miner.py line 214 — use literal replacement to match get_content_as_tokens:

Before (regex — breaks on metacharacters):

log_message = re.sub(delimiter, " ", log_message

After (literal — consistent with get_content_as_tokens):

log_message = log_message.replace(delimiter, " ")